Safety, precision and speed are essential to successful medical procedures. Furthermore, the less invasive a medical procedure is, the greater are the prospects that the patient will recover quickly and without complications. For example, because of its success and relatively low level of invasiveness, the medical procedure known as angioplasty has become a widely accepted method for opening obstructions ("stenoses") throughout the vascular system, particularly in the coronary arteries. The most common form of angioplasty practiced to date is known as percutaneous transluminal coronary angioplasty (PTCA).
In virtually all forms of PTCA, a dilatation catheter having an inflatable balloon at its distal end is guided into a patient's artery and maneuvered within the artery until the balloon is positioned across the narrowing stenosis responsible for inadequate blood flow to the heart. The balloon is then inflated for a brief period, usually for no more than a few minutes, in order to displace or remodel the plaque or other obstruction causing narrowing in the artery. The deflated catheter is withdrawn when the stenosis has been opened and blood is once again flowing adequately. Thus, in contrast to the serious risks and complications previously associated with open-heart surgery, PTCA can be utilized to open blocked coronary arteries using only a small vascular incision through which the dilatation catheter is inserted and operated.
In most forms of angioplasty the dilatation catheter is guided into position through the patient's arteries using a flexible guide wire of very small diameter. Typically, guide wires are formed of surgical grade stainless steel with a diameter on the order of 0.25-0.46 mm (0.010 to 0.018 inches) and an overall length of approximately 175 cm. The distal end of the guide wire, that is, the end that enters the patient and is farthest away from the physician, is typically extremely flexible and may be formed as a coil of very small diameter wire. The end may also be slightly curved in order to make it easier for the physician to maneuver the guide wire around and through bends and junctions in the artery as the arterial pathway is particularly convoluted and branched near the heart.
Once the guide wire is positioned across the target lesion, that is, the site of the stenosis, an appropriately sized dilatation catheter is slid, or "advanced" over the guide wire (hence the common designation of this arrangement as "over-the-wire"). At this point in the procedure the dilatation balloon, which is a portion of the catheter, is deflated and has a minimal cross-sectional diameter; this in turn makes it easier to position the balloon across the lesion before inflation. At various times throughout the procedure, radiopaque dyes are injected into the artery so that the cardiac physician, by watching a fluoroscope, can see the catheter's position in the artery, and can know when the balloon is properly in place.
One difficulty that may be associated with "over-the-wire" dilatation catheters is that unless the catheter and guide wire are positioned simultaneously the guide wire is positioned across the lesion before the catheter. In order to control the catheter the guide wire must extend outside the patient's body far enough to enable the catheter to be threaded along the wire without disturbing the positioning of the guide wire across the lesion. Similarly, if it becomes necessary to exchange or replace the dilatation catheter with a second catheter or device it is equally desirable to retain control of the guide wire access across the lesion.
The most obvious way to address these problems is to increase the length of the guide wire to ensure that a sufficiently long portion of the guide wire extends outside the patient's body. This can be accomplished in two ways. First, a guide wire extension may be "docked" or joined to the proximal end of the guide wire (the end closest to the physician) extending outside of the patient. Because the average dilatation catheter ranges from 120 cm to 160 cm in length, the guide wire extension must be of comparable length. As a result, the guide wire extension is awkward to handle and manipulate. Additionally, following positioning or exchange of the catheter the guide wire extension must be disconnected and moved out of the vascular physician's way. Further complicating matters, the junction between the proximal guide wire end and the docked extension may interfere with the smooth sliding of the catheter along the guide wire, decreasing the physician's control over the procedure.
Alternatively, an exceptionally long guide wire, on the order of 300 cm, can be used. This eliminates the problems associated with guide wire extensions and the additional docking and undocking steps. However, as with guide wire extensions the physician may need additional medical assistance just to monitor or manipulate the lengthy guide wire or may add the additional step of exchanging the long guide wire for a shortened wire following placement of the catheter.
A number of alternative dilatation catheter designs have been developed in an attempt to reduce or eliminate these problems. For example, "fixed-wire" dilatation catheters having a pre-positioned internal guide wire fixed to the catheter have been used. These designs have proven quite maneuverable and relatively easy to position as the internal guide wire provides an additional degree of pushability and torqueability to the unitized device. However, to date such "fixed-wire" catheters have been unable to provide wire guided access to recross a lesion in the event of catheter failure or complications. Thus, even if it were possible to disconnect the catheter from the internal guide wire it would be necessary to utilize a lengthy guide wire or dock an exchange wire in order to retain guide wire access with such catheter designs.
Yet another alternative catheter design is the "monorail" variant of the over-the-wire system. Such a design is disclosed in U.S. Pat. No. 4,762,129 (Bonzel, Aug. 9, 1988). Catheters in a monorail system have two bores or "lumens." The balloon is inflated through one lumen and another, shorter, parallel lumen is threaded over the guide wire. This design enables the short, externally accessible monorail or guide wire lumen to be threaded over the proximal end of a pre-positioned guide wire without the need for docking a guide wire extension.
Regardless of the system, however, when a catheter must be removed from a guide wire, it should be possible to do so in a well-controlled manner quickly, easily, and safely without sacrificing the safety of guide wire access to the target lesion. It should also ideally be possible for a single physician to operate or remove the catheter without the need of an assistant.
More recent "rapid exchange" catheter designs directed to the elimination of unwieldy guide wire extensions have utilized a dedicated guide wire lumen provided with an overlapping longitudinal split seam. A specially designed proximal fitting is utilized to open this seam and direct the guide wire into the lumen as the catheter is advanced. This design enables the vascular physician to remove the catheter by simply grasping the proximal fitting and pulling the catheter off of the guide wire. An obvious drawback of this design is that it adds undesirable bulk to the catheter profile as well as undesirable complexity to the proximal fitting arrangement. Additionally, the split seam makes it possible to unintentionally remove the guide wire from the catheter.
Another possible method for stripping a catheter from a guide wire is simply for the physician to cut the catheter off with a scalpel or a knife as he (or an assistant) pulls it off the guide wire. This procedure is not as simple as it may appear. First, if the guide wire is to stay in position, this procedure usually requires an assistant. Second, quick removal of the catheter using a sharp, bare blade increases the risk that the physician will cut himself.
Along the lines, U.S. Pat. No. 4,997,424 (Little, et al., Mar. 5, 1991); U.S. Pat. No. 4,687,469 (Osypka, Aug. 18, 1987); and U.S. Pat. No. 4,631,059 (Wolvek et al., Dec. 23, 1986) all describe devices for cutting "introducers" from catheters. An introducer is a thin, tube-like device that is used to aid insertion of the surgical apparatus such as a guide wire, with or without a catheter, into the artery or vein of a patient. The introducer is typically much stiffer than the distal end of a guide wire.
The guide wire, one will recall, is preferably as thin as possible, and its distal end is not suitable for pushing through the patient's skin, underlying muscular tissue, etc., and through the wall of the artery. Indeed, were the distal end sharp enough to do so, it might also be sharp enough to penetrate the wall of the artery as it is advanced within the artery toward the heart. Instead, an introducer is first pushed into the artery in order to provide an internal channel through which the guide wire can be fed. The catheter, assuming the assembly was not "fixed wire," can then be threaded over the guide wire within the introducer.
The devices described in the Little, Osypka and Wolvek patents all deal with the problem of removing the introducer once the various clamps, connectors, hubs, and other attachments are mounted on or around the guide wire and catheter. Using either the Little or the Osypka device, the physician lays a generally U-shaped channel of a guiding support portion on the surface of the catheter, so that a separating, forward edge fits between the outer surface of the catheter and the inner surface of the introducer. The physician then pushes the device along the catheter, whereby an exposed blade slits the wall of the introducer to strip it away from the guide wire and catheter. The Wolvek device operates similarly, but it is a two-piece device that must be assembled around the introducer using a hinge.
These known devices are ill-suited for use in stripping a catheter from a guide wire. First, a physician attempting to use the Little and Osypka cutters would have to use great care to hold the channel-like supporting members against the long, thin, flexible guide wire while pulling the catheter with the other hand. Second, the exposed, presumably very sharp blades of these devices are a hazard to the physician and staff, especially during angioplasty operations where speed is essential. Third, each of these cutters is separate from the rest of the catheter/guide wire assembly, and thus represents yet another device that must be sterilized and kept track of separately in the operating room. Fourth, because the typical dilatation catheter is provided with a hard plastic Y-connector, it would be necessary to make the Y-connector removable because it would interfere with cutting the device.
The principal object of the invention is therefore to provide a device that enables a physician to strip catheters, even those with a uniform wall thickness, from a guide wire so quickly, easily and safely that it is well-suited for use during angioplasty operations. Another object is to avoid the disadvantages of guide wire extensions, docking, lengthly guide wires or an exposed blade when stripping the catheter from a guide wire.